1. Field of the Invention
The present invention pertains to an adhesive composition for producing a series of unit set multi-ply carbonless copy paper forms from a stack (lift) of collated sheets. More specifically, the invention relates to a novel adhesive composition which is applied (padded) to the edge of the lift. The edge is then dried, and the lift is separated into individual multi-ply carbonless paper forms.
2. Description of the Prior Art
For many years carbonless copy paper has been made into form sets from a lift of collated sheets by applying an adhesive to one edge of the lift, drying the padded edge and fanning the lift into individual form sets. British Pat. No. 1,263,510 discloses an improvement in edge-padding performance by using as the adhesive a mixture of an aqueous solution of a gelatin derivative and an aqueous emulsion of a polymer. Further improvements in edge-padding are taught in U.S. Pat. Nos. 3,960,638; 3,963,553; 3,970,500; 3,970,501; and 4,041,193 where a naphthalene sulfonic acid-formaldehyde condensate is used in an edge-padding adhesive formulation in various combinations with materials such as water-soluble polymers, water-soluble binders, water-soluble metal salts, polymer emulsions, surface active agents and latexes. Japanese Patent Publication Nos. 12844/1978 and 12845/1978 teach the use of a surface active agent with an aqueous solution of a synthetic polymer adhesive or an aqueous emulsion of a synthetic polymeric adhesive, respectively, in an edge-padding adhesive formulation. Japanese Patent Disclosure No. 99635/1974 teaches an aqueous edge-padding adhesive composition comprising a vinyl acetate-maleic acid copolymer and various alcohols.
U.S. Pat. No. 3,963,553 discloses edge-padding adhesive compositions comprising latex emulsions, water-soluble metal salts and organic solvents. However, there is no teaching therein concerning the criticality of the selection of type and amount of the metal salt and the time of addition as these factors relate to coagulation of the latex and hence to inoperability of the system. Also, the organic solvents disclosed do not relate to water miscibility and resulting homogeneity, a requirement for satisfactory performance in a water-based edge-padding adhesive composition.
U.S. Pat. Nos. 3,779,857 and 4,055,694 disclose the use of borax as an extender in latex compositions for use in coating and laminating textiles. There is no teaching or suggestion of the use of such compositions as edge-padding adhesives.